1. Field of the Invention
The present invention relates to a sipe blade for forming a sipe with one end opened and the other end closed in a land portion on a tread surface of a tire, and to a tire molded using the sipe blade.
2. Description of the Related Art
Conventionally, a heavy load pneumatic tire is formed with a plurality of cuts called sipes in a land portion such as a block or rib formed in a tread surface of the tire in order to increase the braking performance and driving performance as well as to reduce irregular wear of the tire. Particularly, the following sipes are effective for reducing the stiffness of the land portion; i.e., both-side-open sipe with open ends at both side walls of a land portion; and one-side-open sipe with one end opened and the other end closed. In the both-side-open sipe, since a land portion is divided into a plurality of small blocks, the stiffness of the land portion may be reduced too much. As a result, heel and toe wear may be generated thereon. In such a case, the one-side-open sipe is employed.
The sipes are formed using sipe blades of a thin plate (hereinafter referred to as a blade) attached to a tire vulcanizing mold (refer to Japanese Unexamined Patent Publication (Kokai) No. 2000-102925, and Japanese Unexamined Patent Publication (Kokai) No. 10-58458). In a blade for forming the one-side-open sipe, the one end thereof is connected to a rib for forming a groove portion, while the other end is in an unsupported state. Therefore, there may occur such a problem that when a bending stress acts on the blade while removing the tire from the mold after the vulcanizing processing, a portion of the blade connected to the rib may function as a fulcrum of a bending deformation, and stress may converge to the connection portion causing a bending, breakage or damage.
Japanese Patent No. 2,890,310 discloses a pneumatic tire formed with one-side-open sipes in which, in order to prevent the stress convergence at a closed end, the thickness of the sipe gradually decreases from the closed end toward the open end so that the thickness of the closed end is larger than the thickness of the open end. However, in the case of such a tire, the thickness of the blade for forming the sipe is thin at the portion connected to the rib, while thick at the front-end portion. Therefore, a large stress converges at the connection portion, and the blade tends to be bent or broken. Moreover, there is a problem that the land portion tends to form a sharp angle near the open end of the sipe causing irregular wear such as river wear on the tread surface.